1. Field of the Invention
This invention relates generally to a semiconductor, and more particularly to a plastic-molded-type semiconductor device in which a plurality of semiconductor chips are sealed or molded in a single resin so as to achieve a compact construction.
2. Description of the Prior Art
Conventional plastic-molded-type (resin-sealed type) semiconductor devices each having a plurality of semiconductor chips sealed in a single resin are disclosed in the following publications:
Japanese Patent Unexamined Publication No. 1-295454 discloses an example in which circuit formation surfaces of two semiconductor chips face each other, and electrode pads of the two chips are directly joined to each other.
Japanese Patent Unexamined Publication No. 2-2658 discloses an example in which semiconductor chips are bonded respectively to front and rear sides or surfaces of a lead frame, and the semiconductor chips and leads are wire-bonded together from opposite directions.
Japanese Patent Unexamined Publication No. 2-15660 discloses a construction which is generally similar to that disclosed in the above Japanese Patent Unexamined Publication No. 1-295454 but differs therefrom in such a structure that a deformation-preventing resin is filled in between two semiconductor chips.
In Japanese Patent Unexamined Publication Nos. 1-295454 and 2-15660 among the above prior art, the production step of directly joining the electrode pads of the two semiconductor chips to each other is required, and there is encountered a problem that the product yield in this production step is low.
As regards Japanese Patent Unexamined Publication No. 2-2658, after the bonding of the semiconductor chip to one side of the lead frame, or after the wire bonding, the lead frame is inverted so as to effect the bonding at the other side. Therefore, the production process is complicated, and also there is a risk that the wires on the reverse surface may be damaged when the bonding at the opposite side is to be effected.
Further, in any of the above prior art publications, the semiconductor chip is adapted to be mounted on a plate member (which is called a "tab") provided on the lead frame. Therefore, the thickness of the semiconductor device is increased. As a result, when the semiconductor device is mounted on a substrate, a space available in the direction of the height is reduced, which prevents a high-density design. On the other hand, in order to make the thickness of the semiconductor device uniform, if the thickness of the resin is reduced, the resin is damaged under a high-temperature condition as when soldering the semiconductor device to the substrate, so that the sealing function of the resin is lowered, which adversely affects the reliability.